When source of sound moves towards a stationary observer, the apparent frequency heard by him

A liquid rises to a height of 2.4 cm in a glass capillary P. Another glass capillary Q having diameter $80 \%$ of capillary $P$ is immersed in the same liquid. The rise of liquid in capillary $Q$ is

The frequency of fourth overtone of a closed pipe is in unison with the fifth overtone of an open pipe. The ratio of length of closed pipe to that of open pipe is

The plates of a parallel plate capacitor are separated by a distance 'd' with air as the medium between them. A dielectric slab of dielectric constant 3 is introduced between the plates so as to increase the capacity by $50 \%$. The thickness of the dielectric slab is